Method of making steel in an open hearth furnace



Dec. 24, 1963 METHOD OF MAKING STEEL IN AN OPEN HEARTH 'URNACEl 2 Sheets-Sheet 1 Filed Aug. 2, 1961 Dec. 24, 1963 M. E. BOYD METHOD 0F MAKIJNG STEEL 1N AN OPEN HEARTH FURACE 2 sheets-sheet 2 Filed Aug. 2, 1961 INVENTOR MORRIS E. BOYD Attorney United States Patent O 3,115,405 METHGD F MAKING STEEL IN AN OPEN IIEARTH FURNACE Morris E. Boyd, Easley, Ala., assiguor to United States Steel Corporation, a corporation of New .lersey Filed Aug. 2, wel, Ser. No. 128,792 8 Claims. (ill. 75-52) This invention relates to open hearth steel making and more particularly to the use of oxygen for steel making in a tilting open hearth furnace.

With the advent of substantial quantities of oxygen available at reasonable cost there have been many proposals for the use of oxygen in making steel. The use of oxygen can be divided generally into two categories. First, oxygen has been used for llame enrichment and second, oxygen has been injected into or onto the bath to refine or aid in refining the charged material. The former is commonly known as combustion oxygen and the latter, bath or metallurgical ogygen. The use of bath oxygen has followed two general approaches. One approach has been the so-called oxygen steel making process in which only oxygen is used to maintain the heat in the charge as well as for refining, and the other has been the use of oxygen to increase the heating capacity of conventional fired furnaces and to aid in the refining.

I have found that by using bath oxygen surrounded by natural gas and conventional end ring in an open hearth furnace each independently at selected times during the steel making process and also jointly during selected times maximum utilization of the advantages of each can be obtained. Particularly with tilting open hearth furnaces where short charge to tap times are possible a substantial reduction in steel making time and cost is obtained.

It is therefore a principal object of this invention to provide a process for making steel in an open hearth furnace where end tiring and bath oxygen are each used independently and jointly.

It is a further object of this invention to provide a process for making steel in a tilting open hearth furnace which employs bath oxygen surrounded by natural gas independently and in conjunction with end tiring.

A more specialized object of this invention is to provide an improved process for refining high phosphorus molten iron in a tilting open hearth furnace with a high slag volume.

Other objects and advantages of the invention will become apparent from the following description and accompanying drawing, in which:

FIGURE 1 is a sectional plan view somewhat schematic of a tilting open hearth furnace;

FIGURE 2 is a view taken along the plane designated by line II-II of FIGURE l;

FIGURE 3 is an elevational view partially in section with parts broken away for clarity of a lance suitable for injecting oxygen and natural gas;

FIGURE 4 is a foreshortened elevational view partially in section with parts broken away for clarity of a burner; and

FIGURE 5 is a sectional View taken along the plane designated by line V-V of FIGURE 4.

One conventional method of using bath oxygen in an open hearth furnace is to provide an oxygen lance and direct oxygen therefrom onto the charge during meltdown, and thereafter inject oxygen under the surface of the molten metal. According to this conventional practice the end firing of the furnace is continued during the entire operation of making the steel with the oxygen being used only to supplement the end tiring.

According to this invention a stationary open hearth furnace, or a tilting open hearth furnace, is employed,

preferably the latter. A suitable conventional tilting open hearth furnace is shown and designated generally as 10. When a prior heat of steel has been tapped from tapping spout Il and slag flushed, a dominant pool is allowed to remain in the hearth I2. The dominant pool consists of a minor portion of the steel and. slag from that heat and is the starting point for the next heat.

After the banks have been fettled the charging of the next heat commences. First, burned lime is charged through charging doors 13 into the dominant pool, and then iron oxide which may be mill scale or iron ore or the like is charged, then scrap is charged. Molten iron is added immediately thereafter. During the charging of the burned lime, iron oxide, scrap, and molten iron, the furnace is end fired through burners Ztl.

A suitable end burner is shown in FIGURES 4 and 5. Each end burner Ztl includes an outer casing ZI. Disposed within the casing 21 is a low pressure gas pipe 22, a high pressure gas pipe 25, and an oxygen pipe 24. A fuel oil pipe 23 is disposed within the high pressure gas pipe Z5, and terminates short of the end of the high pressure gas pipe wherein an atomizing nozzle 26 is provided. Water inlet pipes 27 and a water outlet pipe 28 are provided to cool the burner. The various pipes have suitable connections to their supplies and regulating device for oxygen, natural gas, fuel oil and water (not shown).

During the charging of the burned lime, iron oxide, scrap and molten iron the ends fired are alternated in a conventional manner. Fuel oil, low pressure gas, high pressure gas and oxygen are used durinfy the charging period.

After the molten iron has been charged, oxygen surrounded by natural gas is injected through at least one and preferably a plurality of lances inserted through Wicket holes ld and submerged in the bath.

A lance suitable for injecting oxygen and natural gas is shown in FIGURE. 3 and designated generally as 30. The lance 30 has an inner pipe 3l having a fluid passage 32 and a concentric outer pipe 33. A uid passage 34 is defined between the pipes 31 and 33. The inner pipe 31 has a connection 35 suitable for attachment to a supply of oxygen and regulating devices (not shown) and the outer pipe 33 has a connection 36 suitable for attachment to a supply of natural gas and regulating devices (not shown). Both the passage 3?. and the passage 34 are open at the end of the lance to permit discharge of the fluid from the passage. The lances are used by inserting them through the wicket holes llt in the charging doors of the furnace. Oxygen is supplied under pressure to the passage 32 and natural gas is supplied under pressure to the passage 34.

The flow of the oxygen in lances is regulated to flow at a rate in all of the pipe to provide at least standard cubic feet of oxygen per hour per ton of steel produced. The flow of the natural gas is regulated in the lances to provide a volumetric ratio of standard cubic feet of oxygen to standard cubic feet of natural gas of at least 3 to l and not more than 8 to l.

The oxygen injected by lthe lance serves several functions. First, it oxidizes a portion of the charged scrap to provide la portion of the iron oxide necessary for refining the steel. Second, it oxidizes the metalloids in the bath providing heat to the charged material. Third, a portion of the oxygen reacts with the injected natural gas providing heat to the charged material. Additionally, the oxygen reacting with the silicon, manganese and carbon in the bath reduces these elements to the desired amount. The natural gas injected by the lance serves two purposes. First, as noted above, it reacts with a portion of the injected oxygen. Second, it acts as a coolant for the lance to prevent rapid `deterioration thereof.

When the oxygen is being injected into the bath the end ring of the furnace is discontinued. However, the injected oxygen and natural gas cause turbulence in the bath which results in a foaming slag condition. It is difficult to work with such a slag and also a foaming slag is relatively inefficient in picking up and maintaining irnpurities. Further, :a foaming slag causes serious erosion of refractories. Therefore, to reduce the foaminess of the slag a high pressure stream of la slag suppressant, preferably natural gas or steam is directed rfrom the end burners across the surface of the slag to suppress the slag. Preferably the rate of high pressure gas ow from the burners is between 18,000 and 32,0100 cubic feet per hour or steam flow of from 800 to 140() pounds per hour. The high pressure gas or steam also serves the additional function of providing a cover for the slag which reduces the Ideleterious eroding of the roof by gases evolved from the slag and molten metal.

When the metalloids have been reduced and the carbon is approaching the desired range the injection of oxygen and natural gas is discontinued and the lances are removed from the bath. To etlciently utilize my process, l have found that the amount of oxygen required for this refining is at least 68'0 standard cubic feet per ton of steel produced. When the injection of the oxygen and natural gas is ceased, the furnace is fired lthrough the end burners 'and the heat finished in a conventional manner. The oxygen refining step of my process is so rapid that it is necessary to discontinue the oxygen and natural gas injection before the carbon has reached the desired level tto `allow the bath to approach equilibrium. The end iir ing is continued until the refining is completed at which time the heat is tapped.

The following is an example of the charging and firing pnactices for a 145 ton heat made according to this invention.

Example A tilting open hearth was end tired at approximately the following rate during charging:

Oil mm. B.t.tu./h1 39.2 High pressure gas mm. B.t.u./hr 32.0 Low pressure gas --mm. B.t.u./hr 22.5 Combustion oxygen cu. ft./hr 25,000

The charging commenced with the addition of burned lime and mill scale in that order. One hundred fty pounds each of mill scale and burned lime per ton of metiallics was charged. The scrap was then charged in an amount equal to about 30% of the total metallics charged and immediately thereafter 100` tons of molten iron was added. At this time three lances were inserted through the wicket holes in the doors. The ow in all lances was regulated to deliver a total of 81100 cubic feet per hour of natural gas and 42,000 cubic feet per hou-r of oxygen.

When the lances were inserted the end firing was stopped and high pressure natural gas was blown from the burners at the rate of about 30,560 cubic feet per hour. About 2 hours and 40 minutes after the lances were inserted they were removed and the end burners red at approximately the following rate:

Mm. B.t.u./ hr. Oil 18.5 High pressure gas 36 Low pressure gas 5 Vwas 2.10 mm. Btu/ton of steel produced, the total oxygen consumed was 95() cubic feet per ton of steel produced, lance oxygen consumed was 750 cubic feet per ton of steel produced, and the production rate was 34.4 tons per hour. h

@ne of the outstanding advantages of this inventlon is the complementary use cf injected oxygen and conventional end tiring to provide a maximum utilization of the benefits of each. During the charging period la maximum amount of heat is delivered to the charged material. When the lances are submerged there is ia sufficient amount of heat generated from the oxidation of the metalloids in the bath and the burning of natural gas to maintain proper temperature for working the heat. There is no need for end firing and hence, end tiring is discontinued. However, the end burners are used to inject a stream of high pressure natural gas or steam across the surface of the slag to suppress the foaming and to protect the roof. When the carbon is approaching the desired level the oxygen injection is ceased and conventional end tiring is used for the final refining of the heat. Hence, during all stages of the making of `the heat of steel the facilities are being used to their maximum benefit and the time is substantially reduced over that of conventional practices. Yet there is no needless duplication in providing heat to the bath. This results in a rapidly produced heat at a minimum cost.

While one embodiment of my invention has been shown and described it will be apparent that other 'adaptations and modifications may be made without departing from the scope of the following claims.

I claim:

1. The method of making a heat of steel in ia basic open hearth furnace comprising the steps of charging the furnace with metal, iron oxide, and basic slag forming material, firing the furnace with fuel 4from end burners over the charged mate-rial during charging thereby forming a bath, `discontinuing the end firing after the charging is completed land injecting oxygen and natural gas beneath the surface of the bath, regulating the flow of oxygen injected to provide a `liow of `at least standard cubic feet per hour per ton of steel produced and regulating the iiow of the natural gas to provide a volumetric ratio of standard cubic feet of oxygen to standard cubic feet of natural gas of at least 3 to 1 rand not more than 8 to 1, during the injection of oxygen and natural gas directing from the end burners across Lthe top of the bath a high pressure stream of a slag suppressant, discontinuing the injection of oxygen and natural gas when the carbon content of the bath approaches the desired amount, thereafter tiring the furnace through the end burners until the heat is refined, and inally tapping the heat.

2. The method of making a heat of steel in a basic open hearth furnace comprising the steps of charging the furnace with burned lime, iron oxide, steel scrap and molten iron, the molten iron being charged last, `tiring the furnace with fuel from end burners over the charged material during charging thereby forming a bath, discontinuing the end tiring after the charging is completed and injecting oxygen and natural gas beneath the surface of the bath, regulating the iiow of oxygen injected to provide a flow of at least 150 standard cubic feet per hour per ton of steel produced and regulating the iiow of the natural gas to provide a volumetric ratio of standard cubic feet of oxygen to standard cubic feet of natural gas of at least 3 to 1 and not more than 8 to 1, during the injection of oxygen and natural gas directing from the end burners across the top of the bath a high pressure stream of a slag suppressant, discontinuing the injection of oxygen and natural gas when the carbon content of the bath approaches the desired amount, thereafter tiring the furnace through the end burners until the heat is refined, and finally tapping the heat.

3. The method of making a heat of steel in a basic open hearth furnace comprising the steps of charging the furnace with burned lime, iron oxide, steel scrap and molten iron, the molten iron being charged last, tiring the furnace with fuel from end burners over the charged material during charging thereby forming a bath, discontinuing the end firing after the charging is completed and injecting oxygen and natural gas beneath the surface of the bath, regulating the flow of oxygen injected to provide a flow of at least 150 standard cubic feet per hour per ton of steel produced and regulating the flow of the natural gas to provide a volumetric ratio of standard cubic feet of oxygen to standard cubic feet of natural gas of at least 3 to 1 and not more than 8 to 1, during the injection of oxygen and natural gas directing from the end burners across the top of the bath a high pressure stream of a slag suppressant selected from a group consisting of steam and natural gas, discontinuing the injection of oxygen and natural gas when the carbon content of the bath approaches the desired amount, thereafter ring the furnace through the end burners until the heat is refined, and finally tapping the heat.`

4. The method of claim 3 wherein at least 600 standard cubic feet of oxygen is injected per ton of steel produced.

5. The method of claim 4 wherein the injected natural gas surrounds the injected oxygen.

6. The method of claim 5 wherein the slag suppressant is natural gas and is directed at a flow rate between 18,000 and 32,000 standard cubic feet per hour.

7. The method of claim 5 wherein the slag suppressant is steam and is directed at a flow rate between 800 and 1,400 pounds per hour.

8. The method of making a heat of steel in a tilting basic open hearth furnace comprising the steps of maintaining a dominant pool from the previous heat which consists of a minor portion of the steel and slag from that heat, charging the furnace with burned lime, iron oxide, steel scrap and molten iron in the order named, tiring the furnace with oxygen enriched fuel from end burners over the charged material during charging thereby forming a bath, discontinuing the end ring after the charging is completed and injecting oxygen surrounded by natural gas beneath the surface of the bath, regulating the flow of oxygen injected to provide a rate of at least 150 standard cubic feet per hour per ton of steel produced and regulating the ow of the natural gas to provide a volumetric ratio of standard cubic feet of oxygen to standard cubic feet of natural gas of at least 3 to 1 and not more than 8 to 1, during the injection of oxygen and natural gas directing from the end burners across the top of the bath a high pressure stream of natural gas, discontinuing the injection of oxygen and natural gas after at least 600 standard cubic feet of oxygen per ton of steel produced has been injected, thereafter ring the furnace through the end burners until the heat is rened, and nally tapping the heat.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Open Hearth Proceedings, A.l.M.E., 1949, vol. 32, pages 79-81 relied on.

Open Hearth Proceedings, All/LE., 1950, vol. 33, pages 51-57 relied on. 

1. THE METHOD OF MAKING A HEAT OF STEEL IN A BASIC OPEN HEARTH FURNACE COMPRISING THE STEPS OF CHARGING THE FURNACE WITH METAL, IRON OXIDE, AND BASIC SLAG FORMING MATERIAL, FIRING THE FURNACE WITH FUEL FROM END BURNERS OVER THE CHARGED MATERIAL DURING CHARGING THEREBY FORMING A BATH, DISCONTINUING THE END FIRING AFTER THE CHARGING IS COMPLETED AND INJECTING OXYGEN AND NATURAL GAS BENEATH THE SURFACE OF THE BATH, REGULATING THE FLOW OF OXYGEN INJECTED TO PROVIDE FLOW OF AT LEAST 150 STANDARD CUBIC FEET PER HOUR PER TON OF STEEL PRODUCED AND REGULATING THE FLOW OF THE NATURAL GAS TO PROVIDE A VOLUMETRIC RATIO OF STANDARD CUBIC FEET OF OXYGEN TO STANDARD CUBIC FEET OF NATURAL GAS OF AT LEAST 3 TO 1 AND NOT MORE THAN 8 TO 1, DURING THE INJECTION OF OXYGEN AND NATURAL GAS DIRECTING FROM THE END BURNERS ACROSS THE TOP OF THE BATH A HIGH PRESSURE STREAM OF A SLAG SUPPRRESSANT DISCONTINUING THE INJECTION OF OXYGEN AND NATURAL GAS WHEN THE CARBON CONTENT OF THE BATH APPROACHES THE DESIRED AMOUNT, THEREAFTER FIRING THE FURNACE THROUGH THE END BURNERS UNTIL THE HEAT IS REFINED, AND FINALLY TAPPING THE HEAT. 